The present invention is directed to telecommunications and especially to handling special number calls from phone sets serviced by a private service provider, such as a private branch exchange (PBX). Special Number services, such as the E9-1-1 voice network in the United States, are based upon an assumption that the origination locus of a special number call is known prior to the initiation of the call. This presumption has traditionally been correct because the specific address and location at an address is associated with every telephone number that supports fully capable special number calling.
For purposes of illustration, by way of example and not by way of limitation, the present invention will be discussed in the context of an emergency service network in the United States, commonly referred to as an E9-1-1 network. The teachings of the present invention are equally applicable, useful and novel in other special number calling systems, such as maintenance service networks, college campus security networks and other networks.
Known location information is used to route E9-1-1 calls to an appropriate Public Safety Answering Point (PSAP). The same information is used by the PSAP to support the emergency response to the call, such as dispatching fire, police or emergency medical personnel and equipment and for call back to the call originator if necessary. Some telephone systems support changing location of telephone instruments within an area, such as within a building, or within a campus or within a local or wide area network. Such telephone systems give rise to significant operational challenges for a special number calling system, such as an E9-1-1 system. When a phone instrument is moved its phone number moves with it, so full support for E9-1-1 calls cannot be provided until up to date location information for the phone instrument is available to a serving E9-1-1 infrastructure to deliver when necessary to the PSAP or other service provider. In prior art communication systems, such updating of location-to-instrument information was effected by a phone user notifying a facilities manager or similar person of the move. The facilities manager entered a database of location-to-number information to update the database to accurately indicate the correct new location-to-instrument information for the recently moved telephone instrument. Often there was a significant time lag between the time the instrument moved and the time the E9-1-1 system was appropriately updated to reflect the change. The greater the degree of telephone instrument mobility that is provided by a system, the greater the strain that is placed on the special number calling networks that serve that system in keeping up with the changes. Voice over IP (Internet Protocol) systems pose significant difficulties for special number network support because of the great degree of mobility that is available for instruments in such a system. Recent developments of data communication systems also permit great mobility for phone instruments. For example, some digital phone instruments used with such data communication networks are capable of connecting with the data communication network and signaling to the network controller their identifying number and authorization for accessing the system. Such mobility may span a building, a campus or even several cities or states. Such communication system capabilities are examples of portability-supporting systems that are particularly difficult to fully support with special number network services, such as E9-1-1 support services.
In the case of a private communications service operator or provider, such as a private branch exchange (PBX), in most situations a unique telephone number associated with an individual instrument “behind” or served by the PBX is not transmitted to the telephone company Central Office serving the PBX and therefore the Central Office cannot differentiate among different instruments subtended to the PBX nor their location when calls are originated from these instruments. The Central Office only is aware of predetermined Pilot numbers that have been associated with the system wide shared circuits interconnecting the PBX and Central Office. This lack of unique telephone instrument awareness can be present even in situations where the Central Office provides the PBX with Direct Inward Dial (DID) service. Determining a particular location within the geographical area serviced by the PBX switch is only possible if the PBX switch somehow notifies the serving E9-1-1 system for relay to the PSAP regarding such location information. Present privately serviced networks do not efficiently or timely inform an E9-1-1 system or PSAP with location information with sufficiently fine granularity to pinpoint the location of a particular phone instrument.
With the coarse granularity presently available to an E9-1-1 PSAP, police or emergency service personnel may go to a location indicated for a particular phone number and find that they have arrived at a large office building or at a widespread college campus with no means available for locating the caller with greater accuracy. In situations involving a corporate PBX the emergency services personnel may respond to a building in an incorrect city or state. Valuable time may be spent in finding the particular locus of the caller to render the required assistance. Such delays can be life threatening in the case of emergency service calls.
There is a need for a system and method for providing appropriate call routing, location and call back information for special number calls, such as E9-1-1 calls from a privately served network, such as a PBX.
There is a need for providing such location and call back information while accommodating mobility of telephone instruments within the privately served network.